Waterproof membrane over Hardiboard needed on walls around tub?

14 years ago

I'm in the middle of a bathroom remodel. It's a simple small bathroom. I installed 1/4" Hardibacker on the floor, including underneath the tub. On the back wall above the tub, (which is an "outside" wall), I installed poly behind 1/2" Hardibacker. Currently the other two walls around the tub just have 1/2" Hardibacker w/o any poly behind them.

In order to ensure it is waterproof and so I use a consistent method, could I just remove the Hardibacker from the two side walls, put up poly, recover the side tub walls with the Hardibacker, then tape the seams (and of course cover the seams with thinset), then tile?

should I remove the polly from the "back" tub wall, put the Hardibacker back up, tape the seams, and use a sheet membrane or Redgard on top of the 1/2" Hardibacker?

Also, IF you recommend using a sheet membrane, is there anywhere to get Kerdi fast? The quickest turnaround I've seen is "we can get it to you in 8-10 days". If I need to get it, I'd like it asap.

Lastly, I'm also going to be tiling the floor. Do I also need to put a waterproof membrane on top of the 1/4" Hardibacker I have on the floor?

I'm a newbie to bathroom remodeling, so I want to make sure that I do this right.

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Comments (4)

diy77
Original Author
14 years ago
Bill or any other experts? please help
pepperidge_farm
14 years ago
If they don't see this, I believe the correct answer is either/or, but not both. You can do a more traditional vapor barrier behind the CBU, OR you can use a membrane. On the floor, if you want it to be waterproof (but that is "extra") you could use Ditra, but the CBU is a good enough tile backer without anything else (if it is over a proper sub floor). Waterproofing aside, Ditra over CBU is overkill.

If you choose to use the Kerdi, tile-experts.com is a great resource, you can call and talk to them about your time limitations, I am sure they would be able to help you out!

Below is a link to a great Kerdi link created by MOngo and saved by weedyacres--- scroll to the bottom for the tub surround pic.

Here is a link that might be useful: Mongo's Tutorial
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diy77
Original Author
14 years ago
Thanks Pepperidge Farm I appreciate it.
bill_vincent
14 years ago
If they don't see this, I believe the correct answer is either/or, but not both.

Yup. The problem is that the vapor barrier should be continuous, meaning all three walls should come down and redo the vapor barrier all the way around.